Modern aircraft utilize fluid transport ducting systems to circulate high-pressure, high-temperature air ported from one of the aircraft turbine engine compressor stages. Because this high-pressure, high-temperature air is diverted or “bled” from a turbine compressor stage, such circulation systems are generally referred to in the art as “bleed air” systems.
For the most part, this high-pressure, high-temperature bleed air is used within the aircraft for deicing the leading edges of wings and stabilizers as well as engine inlets. Bleed air is also used for cabin pressurization and cabin heating.
Because bleed air may exceed temperatures of 1,350 degrees Fahrenheit it is an excellent high-volume, high-capacity heat source which readily meets the above-mentioned aircraft needs. Unfortunately, such elevated temperatures are well above the safe operating limits of the materials typically used in aircraft construction. For example, the structural properties of aluminum alloys used in aircraft structures are degraded above 350 degrees Fahrenheit. Similarly, most modern aircraft type composite materials cannot be safely used in environments above 250 degrees Fahrenheit. Thus, aircraft bleed air systems must be fabricated to avoid any risk of high pressure, high temperature bleed air leakage.
Aircraft bleed air duct systems utilize a network of sealed ducts structured to withstand system pressures and temperatures. For increased safety and reliably, the ducts are further surrounded by refractory insulation which in turn is surrounded by a metallic or composite material gas impervious shroud. This surrounding shroud serves to provide a redundant seal for the bleed air ducts thereby increasing safety and reliability. In addition, the outer shroud tends to confine and collect bleed air leaking from the interior duct. Taking advantage of this behavior, practitioners in the art have devised various bleed air leak detection systems which are designed to port bleed air leaking into the space between the shroud and the duct and to direct it toward temperature sensors. The sensors, in turn, respond and trigger appropriate alarms to alert the aircraft crew.
It will be understood that the primary design consideration exercised in fabricating bleed air leak detection systems is the effective sensing of any leakage within the bleed air system. Notwithstanding this primary consideration, a secondary consideration arises which is also important. This consideration concerns the avoidance of false triggering of bleed air leakage alarms. Unplanned landings, aborts and schedule delays caused by false alarms within the bleed air leak detection system negatively impacts airline efficiency of operation and passenger inconvenience.
Faced with the need to provide reliable, safe and effective bleed air leak detection systems, practitioners in the art have provided a variety of leak detection and monitoring apparatus. For example, in what is perhaps the most traditional bleed air leak detection system, a pair of temperature sensitive wires are supported along the outer shroud of the duct system. Each wire includes a coaxial inner and outer conductor set separated by a eutectic salt which is nonconductive as normal temperature but which becomes conductive when melted. One or more apertures are formed in the shroud near the temperature sensitive wires. The object is to direct leaking high temperature bleed air which accumulates within the shroud toward the temperature sensitive wires. In response to a flow of high temperature leaking bleed air, the eutectic salt melts becoming conductive and forming a short circuit between the inner and outer coaxial conductors. The resulting short circuit triggers a cockpit alarm.
U.S. Pat. No. 7,155,961 issued to Fernandes et al sets forth a BLEED LEAK DETECTION SYSTEM having a cuff secured over a circumferential cut in the duct shroud and underlying insulation. The cuff further supports a manifold in communication with the cuff to define a conduit which collects hot air from a bleed air system leak. A pair of heat sensitive wires are coupled to the manifold and are thus subjected to high temperature bleed air leaking from the interior duct.
U.S. Pat. No. 4,750,189 issued to Lacaster et al sets forth a DUCTED FLOW LEAK DETECTION arrangement for detecting and isolating leaks in a high temperature ducted flow system such as an aircraft bleed air apparatus. The arrangement is configured such that leaking bleed air is contained within the insolating air space of the duct system and constrained to flow to one predetermined end of the duct system. The leaking bleed air is ejected through a fluid outlet opening positioned in close proximity to leak sensing means.
U.S. Pat. No. 7,716,967 issued to Woods et al sets forth a LEAK DETECTOR SLEEVE formed of elastomeric material which is placed upon and encircled a flanged joint forming a gas tight seal thereon. The sleeve includes a hole that communicates with a gap in the flange joint thereby allowing the tip of a sniffer probe to be placed in or near the hole for detection of leakage.
U.S. Pat. No. 5,461,904 issued to Baker sets forth LEAK DETECTION MEANS AND METHOD that directs any leaked fluid from a fluid system joint to a single preselected radial point thereon. A suitable sensing device is located at the preselected radial point.
U.S. Pat. No. 4,655,607 issued to Kern et al sets forth a HIGH SPEED HOT AIR LEAK SENSOR for sensing jet engine bleed air leaks in an aircraft. Infrared detectors are combined with thermal re-radiating elements which are installed in air passages adjacent to the bleed air ducts and downstream of the region where the air bleed leak may occur.
U.S. Pat. No. 7,509,841 issued to Spaolonzi et al sets forth a FLEXIBLE LEAK DETECTION SYSTEM AND METHOD FOR DOUBLE CARCASS HOSE which is supported upon a hole line segment. The leak detection system is supported upon the outer containment carcass of the inner carcass and includes an internal housing chamber in fluid communication with the collection space between the inner and outer carcass. A system sensor is supported upon the housing and is in communication with the collected fluid.
Published patent application US2010/0158068 filed on behalf of Montero sets forth a BLEED LEAKAGE DETECTION SYSTEM AND METHOD having an arrangement of thermostats that are capable of detecting the location where bleed air leakage is occurring. The system provides continuous monitoring of thermostat sensor wiring during flight and thermostat self test function prior to flight.
While the foregoing described prior art devices have to some extent improved the art and have in some instances enjoyed commercial success, there remains nonetheless a continuing need in the art for ever more improved, safe, effective and reliable bleed air leak detection systems for operation within aircraft, spacecraft and the like.